1. Field of the Invention
The present invention relates to a heating resistor element, a manufacturing method for the same, a thermal head, and a printer.
2. Description of the Related Art
Conventionally, in a heating resistor element provided in a thermal head of a printer, in order to improve heating efficiency of a heating resistor and to reduce power consumption, a hollow portion is formed in a region opposed to the heating resistor, and the hollow portion is caused to function as a heat insulating layer having low heat conductivity, thereby controlling an amount of heat flowing from the heating resistor to an insulating substrate side (for example, see JP 2007-83532 A).
As a method of forming the hollow portion, there is employed a method of subjecting a silicon substrate to etching or laser processing, and forming a concave portion (having a depth of 1 μm or more and 100 μm or less) to bond thin plate glass (having a thickness of 10 to 100 μm) serving as a heat accumulating layer thereon through anodic bonding performed at a temperature of 700° C. or less. In this case, it is difficult to manufacture or handle the thin plate glass having a thickness of 100 μm or less, and thus thin plate glass having a thickness, which is relatively easily handled, is bonded to a surface of the silicon substrate, and then a surface of a side opposite to a bonded surface is chipped by etching or polishing to obtain a desired thickness size.
However, the thin plate glass anodically bonded to the silicon substrate is generally soda glass or Pyrex (registered trademark) glass containing an alkaline component, and has the following problems.
That is, in the case of using cheap soda glass, a difference in coefficient of thermal expansion between the silicon substrate and the thin plate glass is large (silicon substrate: 3.3×10−6/° C., soda glass: 8.6×10−6/° C.), and thus warp or distortion occurs in the heating resistor element after the bonding step or during use as the thermal head, which changes contact with thermal paper to deteriorate printing quality.
In contrast, because Pyrex (registered trademark) glass has substantially the same coefficient of thermal expansion (3.2×10−6/° C.) as that of the silicon substrate, the above-mentioned inconvenience hardly occurs, but there are problems in that the material is costly and that processibility thereof is poor. That is, an etching rate of Pyrex (registered trademark) glass is about a tenth of that of the soda glass, and hence it is difficult to process Pyrex (registered trademark) glass to obtain a desired thickness size through etching, polishing, or the like.